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Journal of Nanomaterials
Volume 2015 (2015), Article ID 215371, 10 pages
http://dx.doi.org/10.1155/2015/215371
Research Article

CaCl2-Accelerated Hydration of Tricalcium Silicate: A STXM Study Combined with 29Si MAS NMR

1School of Transportation Science and Engineering, Harbin Institute of Technology, Harbin 150090, China
2Department of Civil and Environmental Engineering, University of California at Berkeley, Berkeley, CA 94720, USA
3Faculty of Science and Technology, Tokyo University of Science, 2641 Yamasaki, Noda, Chiba 278-8510, Japan

Received 20 August 2015; Revised 5 November 2015; Accepted 16 November 2015

Academic Editor: Jin-Ho Choy

Copyright © 2015 Qinfei Li et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The effect of calcium chloride (CaCl2) on tricalcium silicate (C3S) hydration was investigated by scanning transmission X-ray microscopy (STXM) with Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra and 29Si MAS NMR. STXM is demonstrated to be a powerful tool for studying the chemical composition of a cement-based hydration system. The Ca L3,2-edge NEXAFS spectra obtained by examining C3S hydration in the presence of CaCl2 showed that this accelerator does not change the coordination of calcium in the calcium silicate hydrate (C-S-H), which is the primary hydration product. O K-edge NEXAFS is also very useful in distinguishing the chemical components in hydrated C3S. Based on the Ca L3,2-edge spectra and chemical component mapping, we concluded that CaCl2 prefers to coexist with unhydrated C3S instead of C-S-H. In Si K-edge NEXAFS analysis, CaCl2 increases the degree of silicate polymerization of C-S-H in agreement with the 29Si CP/MAS NMR results, which show that the presence of CaCl2 in hydrated C3S considerably accelerates the formation of middle groups () and branch sites () in the silicate chains of C-S-H gel at 1-day hydration.